NAME
loader – kernel bootstrapping final stage
DESCRIPTION
The program called loader is the final stage of FreeBSD's kernel bootstrapping process. It is responsible for bringing the kernel, kernel modules and other files into memory. It creates a set of sh(1) like environment variables that are passed to the kernel. It executes boot scripts written in one of several interpreters. Together with the scripts, it controls the booting process and interaction with the user.
It provides a scripting language that can be used to automate tasks, do pre-configuration or assist in recovery procedures. This scripting language is roughly divided in two main components. The smaller one is a set of commands designed for direct use by the casual user, called "builtin commands" for historical reasons. The main drive behind these commands is user-friendliness. The larger component is the scripting language built into the boot loader. FreeBSD provides three different interpreters: Forth, Lua and Simple. The Forth loader is based on an ANS Forth compatible Forth interpreter based on FICL, by John Sadler. The Lua loader is a full Lua interpreter from https://www.lua.org/. The Simple loader only interprets a list of builtin commands without any control structure.
During initialization, loader will probe for a console and set the console variable, or set it to serial console (“comconsole”) if the previous boot stage used that. If multiple consoles are selected, they will be listed separated by spaces. Then, devices are probed, currdev and loaddev are set, and LINES is set to 24. Finally, an interpreter specific file will be executed.
BUILTIN COMMANDS
The commands common to all interpreters are described in the loader_simp(8) “BUILTIN COMMANDS” section.
The following commands are only available in loader_lua(8) and loader_4th(8):
- be-list
-
Lists the boot environments that are visible to loader. The listed names may be used directly with be-switch.
- be-switch beName
-
Switch to the beName boot environment. The loader configuration will be reloaded from the new root, and any previously loaded kernel and modules will be immediately unloaded.
- boot-conf
-
Load the loader config and commence the autoboot sequence.
- read-conf file
-
Load the specified configuration file.
- reload-conf
-
Revert any previously applied settings, and reload the configuration. Set comands that were executed at the command line to override variables previously set by loader.conf(5) configuration will also be reverted, along with any module options that were toggled.
- enable-module kmod-name
- disable-module kmod-name
- toggle-module kmod-name
-
Enable, disable, or toggle loading of the kernel module named “kmod-name”.
- show-module-options
-
Describe all modules the loader is aware of, and show if they are enabled or not.
The following command is only available in loader_lua(8):
- disable-device device
-
Set a newbus hint to disable the device.
BUILTIN ENVIRONMENT VARIABLES
The environment variables common to all interpreters are described in the loader_simp(8) “BUILTIN ENVIRONMENT VARIABLES” section.
SEE ALSO
libsa(3), loader.conf(5), tuning(7), boot(8), btxld(8), loader.efi(8), loader_4th(8), loader_lua(8), loader_simp(8)
HISTORY
The loader first appeared in FreeBSD 3.1. The loader scripting language changed to Lua by default in FreeBSD 12.0.
AUTHORS
The loader was written by Michael Smith ⟨[email protected]⟩.
FICL was written by John Sadler ⟨[email protected]⟩.
Warner Losh ⟨[email protected]⟩ integrated Lua into the tree based on initial work done by Pedro Souza for the 2014 Google Summer of Code.